In the field of mobile handheld devices, for example, mobile navigation systems, mobile personal digital assistants and mobile phones, especially so-called smart phones, there is a need and design trend to larger displays. The displays of these devices are usually provided with a touch sensitive surface for detecting a user touching a surface of the display for operating the device. However, the overall size of the devices is required to be small enough to be held in a comfortable way within one hand and to be stowed in a pocket or in a small handbag. Therefore, the bezels around the displays of mobile devices are getting smaller or they may be completely omitted. For example, the whole front surface of a mobile phone may be covered by the display or touch screen.
FIG. 1 shows such a mobile handheld device 10, for example a smart phone, having a touch screen 11 comprising a touch sensitive surface covering the whole front surface of the mobile handheld device 10. As can be seen from FIG. 1, the fingers of the hand which holds the mobile device 10 may touch the touch screen 11 and this may be detected by a capacitive touch sensor and may cause usability problems. In the example shown in FIG. 1, the mobile handheld device 10 is held between fingers 40 to 42 on the left-hand side and the thumb and the part of hand palm 43 on the right-hand side. Due to holding the device as shown in the example of FIG. 1, the finger tips of fingers 41 and 42 are touching the touch screen 11 in areas 31 and 32, respectively, and the part of the hand palm 43 touches the touch screen 11 in area 33.
Therefore, there is a need to distinguish a touch of fingers holding the mobile handheld device from a touch of fingers which are actually interacting with a user interface of the mobile device.